Both incidents happened on August 11 last year as police officers in London dealt with the fallout of the riots sweeping the capital.
Last week sources confirmed Pc Alex MacFarlane of the Metropolitan Police had been suspended after a recording was made of a suspect being called a “n.....”.
The arrested man, named as Mauro Demetrio, 21, from Beckton, east London, was arrested on suspicion of drug driving but no action was later taken.
He recorded the abuse on his mobile phone.
The Guardian has reported that another officer, who it said was with Pc MacFarlane when Mr Demetrio was abused, was placed on restricted duties after later being allegedly seen kicking the 15-year-old black boy to the ground and kneeing him.
The incident was said to have happened in the custody area of an east London police station with part of the incident recorded on CCTV.
An independent investigation into the alleged assault on the teenager ended last week and a report, understood to recommend disciplinary action, has been submitted to the Metropolitan police, the Guardian reported.
A Metropolitan Police Spokesman said: “This matter was referred to the IPCC and the officer placed on restricted duties pending the outcome of their independent investigation.
“We have now received their findings and recommendations which we will consider and respond to.
“The decision about who is investigated as a result of a complaint and who is treated as a witness is a decision for the investigators, in this case the IPCC.
“The status of an officer who is under investigation is carefully considered by the MPS on a case by case basis taking account of the circumstances and in line with national police regulations.
“The decision is reviewed on a 28 day basis in consultation with the IPCC when they are investigating the matter.
“When an investigation has concluded, and if an officer is found to have failed in the high standards expected of them, then we will instigate misconduct proceedings.”
Referring to both incidents, Commander Peter Spindler of the Directorate of Professional Standards said: “We are taking these allegations extremely seriously.
“Any use of racist language or excessive use of force is totally unacceptable; at the conclusion of any criminal proceedings we will instigate the appropriate internal action.”